Synthesis and evaluation of the catalytic activity of Ni, Cu, and Zn-doped α-Fe2O3 microspheres for N-formylation of aromatic amines

A simple synthetic method was developed to fabricate three transition metals (M = Ni, Cu, and Zn) doped α-Fe₂O₃ catalysts via a solvothermal approach eliminating the need for a precipitation agent. The synthesized nanocatalysts were characterized using XRD, FT-IR, FE-SEM, EDS, and UV–Vis techniques, and their activity was optimized for the N-formylation of aniline under solvent-free conditions at room temperature. A study of surface morphology revealed that we successfully prepared microspheres of α-Fe₂O₃, Ni–Fe₂O₃, Cu–Fe₂O₃, and Zn–Fe₂O₃. All forms doped represented higher catalytic activity compared to the pristine α-Fe₂O₃, due to a synergistic effect resulting from the presence of transition metals along with Fe. Among all the as-synthesized doped catalysts, Cu–Fe₂O₃ showed the highest activity due to the greater electronegativity of Cu compared to that of Ni or Zn. Thus, Cu–Fe₂O₃ nanocatalyst was selected for the chemoselective transformation of various amines to the corresponding formamides as a sole product (average reaction time: 14 min, average conversion: 90%, average TOF: 0.42 min^–1). Finally, the catalyst could be reused for up to six runs without notable decrease in its activity.